I've got my Silverstone LC-10 case (same one as Dragon uses) and I'm disapointed that the case is noticeably louder than the Antec tower that I was using before.
I have disconnected the twin exhaust fans, but the 80mm front intake fan is still there. And it seems to be the noisiest one. I've got a Zalman "Fan Mate 2" variable speed controller that came with my Zalman CPU cooler. But Since the front fan is so much noisier than the CPU fan, I'm thinking of putting the Fan Mate on that one instead. But I'm also getting a 92mm Zallman fan to replace the Silverstone fan with, hoping that it'll be quieter anyway. I'm also replacing the northbridge fan with a Zalman heat sink (fanless).
So ok, here are my questions:

1) Rear Exhaust Fans. I've removed them, like they do with the Dragons. But now I fear that the open grills are being counter-productive. Instead of pulling air out, they could allow the PS fan (120mm SilverStone) to pull air directly from the (now defunct) exhaust grills, which is a shorter and mostly useless path. I'm thinking of blocking them off, with duct tape if necessary. This will ensure that the air path draws more closely with the original case design (intake from the front and sides, over the CPU, and out the back).

2) Make the PS fan work harder. The Mobo has some temperature thresholds, where I think it'll speed up the PS fan (control leads plugged into sysfan1, I think) when the temperature gets to 150. I've never seen much over 105F. Since this is a larger, more efficient fan, maybe it's quieter overall if I let it do more work, and cut back on the noisy case intake fan. Good idea?

3) Here are my temps, from: mbmon -f and mbmon (c) respectively:

F: Temp.= 100.4, 99.5, 66.2; Rot.= 1704, 1318, 7670
C: Temp.= 38.0, 37.5, 20.5; Rot.= 1704, 1308, 7758

As you can see, the Northbridge is just ridiculous.
How far can I push it with the heat? i.e. at what point do I have to worry?

BTW, I think I found some good deals on stuff from www.svc.com
Zalman ZM-NB47J Northbridge Heatsink $5.85
Spire DualSpeed PCI Dual Fan Speed Controller $8.99
Zalman ZM-F2 92x25mm Adjustable Case Fan 38/53CFM 20/36dBA $5.99
I paid about $7.00 shipping. Stuff is on its way.

I'm thinking that with the 92mm Zalman fan up front, set to 1/2 speed, getting rid of the Northbridge fan, and fine-tuning the VGA and CPU fans with the controllers, I'll be in good shape.

Right now, it sounds like a hair dryer.

BTW, other thoughts on the SilverStone:
Looks great, but they didn't go to much trouble to make it convenient/quiet.

Cons: Case removes with 4 cheap case screws, no thumbscrews in sight. Drive cage mounts with screws, no quick-release.
No rubber mounts for drives. No soundproofing of any kind inside. And I was expecting some sort of acomodation for flash media - a hidden floppy bay perhaps? Nope.

Pros: Heavy machined aluminum front. Gotta love it.
Includes aluminum bar with sticky tape to dress up your DVD drive. Nice aluminum buttons for power/reset/eject.
Cool blue LEDs for power/HDD. Invisible unless lit. Nice and dim, not overwhelming.
Front FireWire port with wiring, 4 front USBs.
Case is sturdy and heavy, attractive feet.

Those actually are not unreasonable. 100F is hot for outdoor weather, but just luke warm for a computer chip. There's not a one that you couldn't touch without burning yourself. My machine runs cooler than that, but it's temps are exceptionally low.

F: Temp.= 82.4, 89.6, 0.0; Rot.= 1035, 746, 1048
C: Temp.= 28.0, 32.0, 0.0; Rot.= 1054, 746, 104

By contrast the older dual Athlon machine at work runs about 49 and 52C even through it sounds like a shop-vac. Still neither one runs as hot as many Prescott series Pentium 4 chips. Your box seems to be running at a reasonable temprature right in the midle of that range. I would say you should start to worry around 60C and throttle by 70C or so.

Thanks TJC, for confirming.

I've modded a bit: I put the fan controller on the Zalman CPU cooler and toned that down, and removed the front intake fan. I blocked off the exhaust fan ports, where the exhaust fans have been removed, so it won't suck air IN through those "out" ports. And I duct-taped half of the side holes on the PS side, so that it'll pull more from the front and other-side, thus drawing most of the air aross the hot chips.
It's a lot quieter already, with the northbridge fan still in place.

Temps during playback:
Temp.= 38.0, 45.0, 30.5; Rot.= 1804, 0, 7670

I found the noise problem in the front end. The fan that they (silverstone) used seems nice - 92mm. The problem is on the other side of the grill. They put all of the electronic crap in the way. The wiring and little boards for the power/reset buttons and LEDs are right there, on the other side of the grill. This obviously obstructs the airflow, and I suspect contributes a lot to the noise. If I pull the fan away from the grill, it's nearly silent. Stick it up to the grill, and it's making a big racket. I'll replace it with the two-speed Zalman fan that I have on order. That should help.

Anyway, thanks for the good advice on the 60-70c range. I should be able to stay well under that, given what I'm seeing/hearing now.

One thing to remember is that you're probably close to the low point for the year as far as ambient (room) temprature goes (at least if you're in the northern hemisphere). How is that going to hold up when the indoor temprature goes up near 100F or even higher? While it's still OK now, I wouldn't be really pleased about the increase in CPU temprature that you're already seeing...